Mysterious Yellow Wagtail at Cape Nanhui, Shanghai

Found at Shanghai’s Cape Nanhui on 1 May 2019: possible White-headed Yellow WagtailMotacilla flava leucocephala. The discovery by Haiming Zhao provoked excitement and uncertainty among Shanghai birders. Certain aspects of the wagtail, notably the pale mottling on its mantle, cast doubt on an identification of White-headed. “Those pale/odd-looking feathers are unusual for leucocephala,” said Gomboo Sundev, a bird-tour leader in Mongolia, where leucocephala breeds. “I have never seen such an individual of the subspecies in Mongolia” (in litt., 2019).

Beijing-based British birder Paul Holt also noted the anomaly: “I was surprised … by the Shanghai bird’s mottled mantle” (in litt., 2019). Per Alström, co-author of Pipits and Wagtails, called the pale feathers on the mantle and scapulars “puzzling” (in litt., 2 May 2019). Both experts noted the pale base to the lower mandible of the Shanghai wagtail, also unexpected in leucocephala.

Students of Yellow Wagtail will not be surprised by the uncertainty. The Yellow Wagtail complex is a “systematic conundrum”; the various subspecies of the complex often “defy separation under the biological species concept” (Tyler 2004, 689). Interbreeding of the various subspecies occurs “freely at overlap zones, producing fertile hybrids” (689), often making it the case that “the direct parentage of Yellow Wagtails cannot be deciphered” (725). There is furthermore the prospect of partial albinism, a phenomenon that can make other subspecies of Yellow Wagtail appear white-headed (Alström & Mild 2003, 80, 269, 282).

In the case of leucocephala, another reason for the uncertainty is the sheer lack of knowledge about the race, even among elite ornithologists. Holt describes White-headed Yellow Wagtail as a “poorly known subspecies” (2019); Alström says his experience with the race is limited to “a few specimens and only one live bird” (in litt., 7 May 2019); Sundev told me he has seen the subspecies only about a dozen times (2019). The lack of information forces even great birders such as Holt to speculate: “The million-dollar question is whether [the mottled mantle and pale basal half of the lower mandible of the Shanghai bird] fit within the range of variation in leucocephala, or are they suggestive or even indicative of less than thoroughbred genes?” (2019)

Why is so little known about leucocephala? The biggest reason is the remoteness of its breeding range. White-headed Yellow Wagtail breeds in sparsely populated northwestern Mongolia, at places such as Khar-Us Lake (48.083328, 92.541368) and Durgun Lake (47.673106, 93.451188) (Sundev 2019). Alström and Mild say the race breeds also in areas adjacent to northwestern Mongolia, such as the Tuva Republic of Russia and “probably … northernmost Xinjiang” (2003, 281). Even the wintering range is uncertain; Alström and Mild say leucocephala “probably winters mainly in India but the exact wintering grounds are not known” (281).

The verdict on the Shanghai wagtail? “I would say it is leucocephala,” Sundev said. Holt agreed: “I would think that these [a White-headed Yellow Wagtail found in Hong Kong in April and the Shanghai wagtail] are the first two records of leucocephala for the whole of eastern China.” Alström, however, was less than fully convinced: “I’m not aware of a leucocephala with such a pale-mottled mantle as the Shanghai bird—although I can’t say they don’t occur” (7 May 2019).

PHOTOS

L: The unusual Yellow Wagtail seen at Cape Nanhui, Shanghai on 1 May 2019. Note the pale mottling on the mantle. R: White-headed Yellow Wagtail Motacilla flava leucocephala, Mongolia. (L: Haiming Zhao; R: Gombobaatar Sundev)‘The encounter with the Western Yellow Wagtail was totally unexpected,’ said Shanghai birder Haiming Zhao, who discovered and photographed the bird. ‘The location where I found the bird is in a big area in Nanhui which has many trees newly planted. I came across this Western Yellow Wagtail when I went by this area searching for buntings. I was in my car looking at the ground 10-15 meters away to the left when I saw this special bird. Its bright gray head and yellow lower body were so eye-catching and had made it easily distinguished out there from a flock of eastern yellow wagtails on the ground’ (Zhao in litt., 2019). (Haiming Zhao)White-headed Yellow Wagtail on the breeding grounds in northwestern Mongolia. (Gombobaatar Sundev)

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Craig Brelsford

Craig Brelsford lived in Shanghai from 2007 to 2018. When he departed China, Craig was the top-ranked eBirder in the country, having noted 933 species, as well as the top-ranked eBirder in Shanghai (323 species). A 1993 graduate of the University of Florida, Craig was an award-winning newspaper editor in the United States for 10 years. In 2002, Craig earned a master's in business administration from the University of Liege in Belgium. Craig lives in Debary, Florida with his wife, Elaine, and their son, Tiny.
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This looks more like a pattern of partial leucism. The pale back feathers argue against leucocephala, and even the pale head coloration deviates from the typical pattern by showing some suspicious dark discoloration on the crown. I think there is an extremely low chance of the first East Chinese leucocephala being a rare plumage variant at the same time. An unfortunate combination of mutations in an Eastern Yellow Wagtail would presumably also be capable of causing this pattern.

Although the head pattern seems to indicate leucocephala, I would hesitate to accept it as such (given the rarity status in the area). Judging from the pattern of the mantle, there is clearly some genetic colour aberration (leucism?) present in this bird, and a white head is a well-known aberration in Yellow Wagtail in other parts of the world. For example, the ‘Channel Wagtails’ in Britain: https://www.the-soc.org.uk/photo-gallery?start=1305

My point is, since it’s clear that this bird has a colour aberration, we should be careful; there is a risk that the head pattern is a product of the same aberration.

It is always good to learn good stuff and see what birder experts would say at shanghaibirding.com, and it is great to see the photos of Motacilla flava leucocephala at breeding area in Mongolia. I also compared with the photo of Western Yellow Wagtail taken in HK on Apr 8, 2019 at ebird. Noted the doubt about pale feathers on the mantle and scapulars and pale base to the lower mandible of the one found in Shanghai on May 1. My question would be whether it is possible to see the photos of non-breeding leucocephala such as in India, or photos of leucocephala that is turning to breeding plumage from non-breeding plumage at any other places other than Mongolia, Hongkong and Shanghai. Would be good to see more photos of leucocephala.

You can find sereval pictures of WH Wag on BirdingMongolia https://birdsmongolia.blogspot.com/
The situation is complicated by the fact that we always find territorial beema and macronyx within the leucocephala range. Per already noted the high degree of variation displayed by leucocephala and that could be caused by gene flow created by those stray non-leucocephala males (we did never dare to ID the females to taxon!).
Aberration can show up in all bird species and hence could be found in leucocephala as well.
I would not accept this bird as a first for any region outside what is considered the normal (though wintering range not known for sure at present) range (breeding and wintering).